Railroads in North America typically consist of a network of railroad tracks. Each of these railroad tracks is typically formed by placing wooden or concrete crossties on top of a bed of gravel ballast, and then attaching a pair of steel rails to the top of those ties. Variations in specific construction methods occur in special function areas such as road and bridge crossings, yards or the like.
One of the major railroad maintenance activities which is undertaken on an ongoing and regular basis is the monitoring and replacement of the crossties beneath the tracks, in order to maintain the integrity and safety of these railroad tracks. While many railroad maintenance tasks have become highly automated over the last number of years, tie replacement is still a task which while being mechanically assisted, is somewhat more labour and logistic intensive in nature at the present time. For example, while there are machines which can be used to in relatively automated or streamlined fashion withdraw and replace individual railroad ties under a track, the actual movement, supply and placement of the ties to be put in place beneath the track remains the difficult portion of the task.
One of the issues which still remains is that there is no efficient or fluid method for the placement of variable numbers of replacement railroad ties in approximate proper position along the railroad right of way for use in replacement activities.
In determining which railroad ties might need to be replaced, a machine can be driven along the track which would exercise some type of mechanical test on each railroad tie or otherwise calculate which tie or ties needed to be replaced and mark them as such. The second method, which is still widely used as well, consists of a track maintenance employee physically walking along the railroad track and, based on visual inspection, marking individual railroad ties that need to be replaced with a paint marking or the like. Once the ties have been marked for replacement, a track gang can then replace the necessary ties in the course of performing maintenance on the track.
Beyond the oldest method of simply walking along or moving along the track with a complete set of equipment, replacing each tie directly as it is inspected, there is not a quick and efficient use of the equipment and crews necessary in these circumstances or applications. As indicated above the most difficult portion of the task of railroad tie replacement in terms of logistics is the distribution of the replacement ties along the railroad right of way so that they can be properly installed by the maintenance crew.
Automatic tie replacement machines can carry very few if any supplies of replacement ties. The majority of those machines are designed to basically replace a tie under the track with a new tie which is picked up from the ground beside the track and installed in position. In certain cases what might have been done in the past to distribute the proper number of replacement ties would be to effectively bring along a truckload or a train load of replacement ties behind the tie replacement machine and use a tractor or the like to drop the ties into approximate position before the tie replacement machine was there to make that particular replacement. However, this makes the actual tie replacement process take longer than if the replacement ties are already in place on the ground beside the track and can simply be picked up in the appropriate position and installed.
One of the methods of distribution of replacement ties rather than bringing along an entire train load of replacement ties with the tie replacement machine has in the past been to effectively come along the track after the ties have been marked for replacement and drop ties in approximate position where they will be used by the following maintenance equipment or tie replacement machine. A distribution crew working separately from the actually tie replacement crew can work more efficiently, as can the replacement crew, if the two jobs are not directly combined or done at the same time.
In circumstances where a large number of ties is required in an area for replacement, that number of ties needs to be dumped beside the track for use by the crew, whereas in other circumstances where fewer ties are required a smaller number of ties might need to be dumped for use, or on a section of track where no tie replacement was required to be done at all, then no replacement ties would be needed for a distance.
Beyond simply dumping replacement ties in approximately the right numbers and approximately the right places, another method which has been practised in the past is to drop a predefined batch or number of ties, or a banded quantity of ties, along the railroad. For example, it is known that certain railroad maintenance companies have banded replacement ties together in groups of 15 (or some other predetermined number), and then they simply count their way along the replacement markings on the track and drop those banded batches of ties along the track in approximately the right place so that they are in position when they are required for use. However, the cost of preparing these banded groupings of ties is significant, and when the replacement ties are banded into these predefined lots they also present somewhat of a limitation insofar as limiting where and how many batches of ties can be distributed, since they can only be distributed in multiples of 15 or whatever the predetermined number is which is in each banded group. This banding approach does save significantly on the time and labour involved in the actual tie distribution process, however the cost of the banding step is significant.
Something which has been done in the past to enhance the banding method is to effectively capture GPS coordinates for each tie which needs to be replaced, and then generating a signal or somehow marking for action the dropping of one of these predefined batches or numbers of ties as necessary. For example, if the ties were batched in units of 15, a marking or location is captured or marked every 15th replacement tie being required, and then a banded number of ties is dropped at that point. However, the ties will be dropped in a large batch at either the beginning or end of a replacement section, and in a particular section of track where not a large number of replacement ties were required, the 15th tie might be a long ways from the first tie needing to be replaced and as such the problem of needing to move the replacement ties around a fair bit for installation then resurfaces.
It is also known that in certain circumstances where this banded approach has been used, the marking crew who are responsible for marking the locations for the dropping of various items and replacement ties need to work in very close physical proximity to the tie distribution crew. This is a significant rate limiting step for the marking crew, since they would not typically spend nearly as much time on a particular section of track testing or identifying ties for replacement as would the maintenance crew who were actually undertaking the job of distribution or replacement. In addition to trying to eliminate the banding system, if it were possible to come up with a method by which the marking crew could work at their own speed independently from the maintenance crews, this would also minimise the cost of the railroad tie replacement task.
Because railroads typically are required to maintain hundreds or thousands of miles of railroad tracks on a recurring basis, tie replacement is a major component of track maintenance. Anything that can be done to streamline the tie replacement process in terms of equipment, materials, traffic control, labour and management would enhance profitability of railroads since tracks would be down for shorter periods of time for maintenance and less cost potentially would be involved in the actual maintenance step. It is contemplated that any type of system which could be created which would enhance the tie replacement function by allowing for the distribution of variable predetermined numbers of replacement ties in close to the right locations along a railroad right of way would be welcome as an optimisation of the tie replacement function of railroad maintenance.